Netanyahu has infuriated the White House and Democrat lawmakers by accepting the invitation by Republicans to speak on Capitol Hill, in what Israel’s Haaretz newspaper calls “the speech of his life”.

Israeli commentators and US officials are saying Tuesday’s speech, two weeks before Netanyahu fights an election for a third consecutive term in office, endangers what has historically been bipartisan US political support.

A string of Democratic lawmakers are voting with their feet, announcing they will not attend.

“The chances of shooting down the (emerging Iran) agreement depend on enlisting a majority of two-thirds of the members of Congress, which could overcome President (Barack) Obama’s expected veto and impose new sanctions on Iran,” columnist Ben Caspit wrote in the Maariv daily.

“After the dirty trick came to light, the number of members of Congress who retracted and who will not support this course of action against their president has grown and the chances of success have dropped,” he wrote.

US National Security Advisor Susan Rice slammed the politicisation of the issue.

“What has happened over the last several weeks by virtue of the invitation that was issued by the Speaker and the acceptance of it by Prime Minister Netanyahu, two weeks in advance of his election, is that on both sides there has now been injected a degree of partisanship,” she said in an interview with public broadcaster PBS.

“I think it is destructive of the fabric of the relationship,” she added.

– ‘Supposed to understand America’ –

Mark Heller, a political analyst at Israel’s Institute for National Security Studies told AFP the entire speech issue has been interpreted as partisan.

“It’s not surprising that the Republicans would try to do that; a little bit more surprising I think that Netanyahu would allow himself to be used that way because he has a reputation as being someone who’s supposed to understand America and someone who’s supposed to understand the importance of bipartisanship in the American-Israeli relationship,” Heller said.

Obama has refused to meet Netanyahu during his visit, and Vice President Joe Biden and Secretary of State John Kerry will both be abroad.

Caspit said Netanyahu’s gambit would be ineffectual.

“Does he really think that one speech will stop the process that the world powers have been maintaining with Iran, will persuade the president, conquer Congress, force China, Russia, Germany and all the others to toe the line with him and immediately cancel these negotiations?”

Even Netanyahu’s coalition partner and cabinet colleague, Foreign Minister Avigdor Lieberman, described the speech as “of no great importance”.

“No agreement will prevent Iran from obtaining nuclear weapons and that is why we must decide on our own and act accordingly,” he said in a television interview.

For most of his political career Netanyahu has warned Tehran wants to acquire nuclear weapons.

In 1996, during his first term as premier, in a speech to Congress he spoke of “unreconstructed dictatorships whose governmental creed is based on tyranny and intimidation”.

He named Iran as “the most dangerous of these regimes”.

“If this regime, or its despotic neighbour Iraq, were to acquire nuclear weapons, this could presage catastrophic consequences, not only for my country, and not only for the Middle East, but for all mankind.”

In 2012 he warned in a Washington speech to pro-Israel lobby group AIPAC, which had in the past opposed new sanctions on Iran, against backing Obama’s negotiation strategy.

“Iran calls for Israel’s destruction and they work for its destruction each day, every day, relentlessly,” he said.

“This is how Iran behaves today, without nuclear weapons. Think of how they will behave tomorrow, with nuclear weapons.”

Netanyahu said on Wednesday that he had no choice but to fight his corner on Capitol Hill.

“I respect the White House and the US president but on a serious subject, it’s my duty to do everything for Israel’s security,” he said.

“Under the agreement that is being prepared, we have reason to worry… if the world powers have reached an agreement with Iran,” he said. -AFP